Liquid agrichemicals have advantages over solid agrichemicals, e.g., granular pesticides, in certain applications. Liquid agrichemicals provide faster response, particularly under dry conditions, and in the case of pesticides provide more effective control of soil insects than solids. Where root uptake is required, as in the application of systemic pesticides, liquids may be the only practical form. Soil application of liquid pesticides avoids the hazards of handling seed which has been pretreated with the pesticide. Moreover, when a liquid pesticide is applied to soil via microtube injection, for example, for control of soil nematodes and insects, very low volumes of pesticide can be used but with great accuracy. Similar benefits accompany the application of other liquid agrichemicals such as herbicides and fertilizers.
In microtube injection of a liquid agrichemical such as a pesticide, the active agent customarily is diluted to a required concentration in a mixing tank and pumped to one or more manifolds which feed a plurality of plastic injection tubes typically having internal diameters of about 0.75-2.00 mm. For effective injection and metering into the soil or into crops, the pesticide must flow from the microtubes in a continuous stream as opposed to spraying or dripping. The continuous flow and low flow rate are achieved by long tube length, the resulting pressure drop being a function of the length as well as the internal diameter of the tubing.
A known microtube applicator is the "Jectarow" system introduced by Agchem Pty. Ltd., Adelaide, South Australia, for application of a liquid, unformulated nematicide having a viscosity equal to or less than water in cereal farming. In this system, a piston pump with pressure relief valve, a pesticide supply tank and microtubes with manifold are mounted on a seed planter for injection of diluted nematicide into furrows during seeding. The pump meters the pesticide and may be driven electrically using a pressure regulator or mechanically by a drive wheel in contact with a ground wheel of a tractor. The microtubes are oriented to rows to be injected by guide tubes mounted below the manifold. A plurality of manifolds connected by tees may be employed, each feeding a plurality of microtubes of equal length, the number of microtubes depending on the number of rows to be injected.
In use, continuous flow of liquid pesticide formulation in the microtubes of the Jectarow apparatus normally prevents blockage by dust or foreign matter which may enter the system. However, if the flow is interrupted (for example, by suspension of application due to sudden storms or overnight delays), the liquid pesticide in the diluted product tends to separate. The microtubes thus clog easily, resulting in substantial economic loss due to down-time for cleaning and/or the expense of replacing components of the microtube applicator system.